A prerequisite of micro-circuit production with a reasonable yield is defect free masks to be used in the production process. Over the past 12 years a number system have been developed, and patented for the automatic inspection of optical masks. (See U.S. Pat. Nos. 4,247,203 and 4,805,123). These systems perform a comparison between two adjacent dice on a photomask or reticle. Similarly, technology has evolved to inspect a die on a reticle against a CADS database. (See U.S. Pat. No. 4,926,487). These optical systems are, however, limited to optical masks because defects on X-Ray masks may not be apparent in the visible or ultraviolet spectra. Furthermore, optical inspection is limited in its resolution capability by the fundamental diffraction limit that of course also limits optical lithography. Even with phase shift mask techniques it is expected line widths below 0.35 microns cannot be achieved with optical lithography techniques and that X-Ray lithography will dominate for line widths smaller than that.
For the inspection of X-Ray masks it is expected that scanning electron microscopy techniques will be employed. Recently companies have experimented with using conventional electron microscopes for the inspection of X-Ray masks. While these experiments have been successful in detecting defects, conventional electron microscopes are much to slow and require highly skilled operators. These two attributes make such systems not practical for use in the semiconductor industry.